INTERNATIONAL
OFTechnology
ELECTRICAL
ENGINEERING
&
International
Journal of ElectricalJOURNAL
Engineering and
(IJEET), ISSN
0976 – 6545(Print),
ISSN 0976 – 6553(Online) VolumeTECHNOLOGY
3, Issue 2, July- September
(2012),
©
IAEME
(IJEET)
ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
Volume 3, Issue 2, July – September (2012), pp. 76-83
© IAEME: www.iaeme.com/ijeet.html
Journal Impact Factor (2012): 3.2031 (Calculated by GISI)
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IJEET
©IAEME
SIMULATION OF SIX PULSE CYCLOCONVERTER EXCITED
INDUCTION MACHINE
Vishnu Goyal, Ph.D Student, Non Member
Dr. Sulochana Wadhwani, Member
ABSTRACT
Cycloconverter is essential for controlling a.c. motors at low speed drives especially in high
power application. This paper discusses the simulink model of six pulse three phase to three
phase cycloconverter controlled induction motor. Cosine firing control circuit used to generate
pulse for different SCR’s of cycloconverter. The logic control circuit of cycloconverter for
positive and negative converter selection circuit has been developed with different types of gates
and pulse generators [1]. In this simulation, time period of pulse generators of converter selection
circuit is changed to control output frequency of cycloconverter. LC filter circuit designed to
reduce harmonics from cycloconverter controlled output voltage [2]. The simulation results show
effects of variable frequency (30Hz to 10Hz) on speed, torque and stator current of three phase
induction machine with different value of LC filter circuit.
Keywords: Simulation, cycloconverter, induction motor, harmonic reduction.
I.
INTRODUCTION
Variable frequency a.c. motor drives have been introduced to increase their use in various
industrial applications. Control of ac motors has become very popular because it is possible to
obtain the characteristics of dc motors by improving the control techniques. The phase control
cycloconverter consist of a dual converter, which is controlled through the timing of its firing
pulse, so that it produces an alternating, rather than a direct output voltage. Cycloconverter can
supply lagging, leading or unity power factor loads while its input is always lagging.
Cycloconverter produce harmonics rich output voltage [3]. When cycloconverter are use to run
an ac machine, the magnetizing impedance of machine is very high for higher order harmonics
[4-5]. The leakage inductance of the machine filters most of the higher frequency harmonics and
reduce the magnitude of the lower order harmonics. Simulation work has been carried out using
MATLAB/SIMULINK [6]. It is important noted that these are not the only harmonics
76
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 3, Issue 2, July- September (2012), © IAEME
that occur at the output of the cycloconverter. Several factors including imperfect timing
on switching and switching control method can induce distortion at different frequencies [7].
The use of cycloconverter also creates adverse affect on the input of the cycloconverter
system. Harmonics are produce in the input current, and the input power factor
can be low depending on the load. These affects are consistent with rectifiers, though
harmonics occur at different interval in cycloconverter than occur in rectifiers [8].
POWER
CIRCUIT
CYCLOCONVERTER
II.
OF
THREE
PHASE
TO
SINGLE
PHASE
Three phases to Single phase full wave cycloconverter is shown in Fig.1 along with it firing
circuit for both power circuit of Positive converter and Negative converter of cycloconverter.
Power circuit of positive converter supplies positive half cycle of output voltage and power
circuit of negative converter supplies negative half cycle of output voltage. The waveform of
output voltage of this cycloconverter shown in Fig.2. The frequency of output voltage is
controlled by using firing and selection circuit of positive converter and negative converter
SCR’s. Power circuit of positive and negative converter as shown in fig.3 and fig.4 respectively
Fig.1 Three phase to single phase Cycloconverter and its firing circuit
77
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 3, Issue 2, July- September (2012), © IAEME
200
150
Voltage
100
50
0
-50
-100
-150
-200
0
0.05
0.1
0.15
0.2
Time
0.25
0.3
0.35
0.4
Fig.2 Output voltage of Three phase to single phase cycloconverter
Three phase input supply for both power circuit of positive and negative converter have three
different voltage sources for three phase with 120° phase difference and 60 Hz frequency.
Fig.3 Power circuit of positive converter
Fig.4 Power circuit of negative converter
A. Firing and Converter Selection Circuit
Detail of firing circuit and converter selection circuit for three phase to single phase
cycloconverter shown in Fig.5. Inside block of SCR converter selection circuit as shown in Fig.6
is design with pulse generator and AND Gates logic circuit.
78
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 3, Issue 2, July- September (2012), © IAEME
Figure 5: Inside block of SCR converter selection circuit
Fig.6 SCR Converter Selection Circuit
Selections of positive and negative converter depend on required frequency of output voltage.
Switching sequence and firing of converters is in non circulation current mode in this simulation,
when positive converter is turn on at that time negative converter is turnoff and when negative
converter is turn on at that time positive converter is turn off. In non circulating current mode of
cycloconverter converter current is equal to load current.
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 3, Issue 2, July- September (2012), © IAEME
III.
THREE PHASE TO THREE PHASE CYCLOCONVERTER WITH RL LOAD
Three identical three phase input to single phase output cycloconverter connected together to
supply three phase load.
Fig.7 Three phase to three phase cycloconverter with RL load
VA
200
0
-200
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0
0.05
0.1
0.15
0.2
Time
0.25
0.3
0.35
0.4
VC
200
0
-200
VC
200
0
-200
Fig.8 Output voltage of three phase to three phase cycloconverter with RL load
80
International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 3, Issue 2, July- September (2012), © IAEME
MATLAB-SIMULINK model of three phase to three phase cycloconverter circuit shown in
Fig.7 and its output voltage wave form for 10 Hz of frequency shown in Fig.8 with R-L load.
IV.
RESULTS & DISCUSSION
The results were taken from the simulation of the delta connected cycloconverter excited
induction motor. Delta connected cycloconverter provides a better harmonics content in the
output line to line voltage due to cancellation of the common mode voltage harmonics between
the outputs. Induction motor is controlled by variable frequency, which is supplied by delta
connected cycloconverter and its filter circuit as shown in Fig.9. Speed, torque and stator current
of phase A, characteristics of induction motor shown in Fig.10 with filter circuit of (L=0.1 mH &
C=1F) at the time of changing frequency they need more time to get in their steady state
condition. Modified filter circuit with filter circuit of (L=0.01mH & C=20F) different
characteristics of induction motor shown in Fig.11 need so less time to get in their steady state
condition at time 0.2 sec frequency changed from 30 Hz to 10 Hz.
.
Fig. 9 Simulink of cycloconverter controlled induction motor
Fig.9 Simulink of cycloconverter controlled induction motor
With Filter Circuit
of L=0.1mH,C=1F
5000
<Speed (RPM)> Frequency changed 30Hz
to 10Hz at 0.2 sec
0
-5000
0
0.05
4
x 10
2
0.1
0.15
0.2
0.25
0.3
<Electromagnetic torque Te (N*m)>
0.35
0.4
0.3
0.35
0.4
0.3
0.35
0.4
0
-2
0
0.05
0.1
0.15
0.2
0.25
<Stator current is_a (A)>
2000
0
-2000
0
0.05
0.1
0.15
0.2
Time
0.25
Fig.10 Speed, torque and stator current characteristics of induction
motor with the filter circuit of L=0.1mH, C=1F
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 3, Issue 2, July- September (2012), © IAEME
With Filter Circuit of
L=0.01 mH,C=20 F
2000
<Speed (RPM)>
Frequency changed
30Hz to 10Hz at 0.2 sec
0
-2000
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.3
0.35
0.4
0.3
0.35
0.4
<Electromagnetic torque Te (N*m)>
500
0
-500
0
0.05
0.1
0.15
0.2
0.25
<Stator current is_a (A)>
200
0
-200
0
0.05
0.1
0.15
0.2
0.25
Fig.11 Speed, torque and stator current characteristics of induction motor with
the filter circuit of L=0.01mH, C=20F
CONCLUSIONS
V.
Delta connected cycloconverter, its firing and control circuits are designed and simulated to
obtain desired results. Torque characteristics of the induction motor that matches with demand
torque characteristic by the use of cycloconverter and its control circuit at the different desire
frequency. High number of pulses will not complicate the control circuits, because it will just
increase the number of these control circuits. Increasing number of pulses will improve the
cycloconverter output waveforms and will decrease the harmonic component values. After
modification of filter circuit, torque and speed characteristics of induction motor at the time of
changing frequency is improved. This contribution will report on the result obtained using
MATLAB-SIMULINK for three phase cycloconverter coupled to an induction motor.
VI.
REFERENCE
[1] Rezgar Mohammed khalil and Maamoon al-kababjie. “Modelling and simulation of
multi-pulse cycloconverter fed AC induction motor and study of output power factor” AlRafidain Engineering, 2007 Vol.15 No.1pp.1-14,
[2] B.R Pelly. ‘Thyristor phase controlled converters and cycloconverters: operation, control
and performance’ Wiley-interscience, New York 1971, 3rd Edition.
[3] Sandeep Pande and Hashit Dalvi. “Simulation of cycloconverter based three phase
induction motor” IJAET July 2011, vol.1, issue 3, pp.23-33,
[4] N. Mohan, Tore M. Undeland and William P. Robbins, Power Electronics Converter
Applications and Design. John Wiley & Sons, INC 2nd Edition.
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International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 3, Issue 2, July- September (2012), © IAEME
[5] Policarpo,J.G de Abreu, S.De sa and C.C. Predo “Harmonics torque in three phase
inductions motor supplied by Non-Sinusoidal voltage” 11th Intl.Conf.2004, Harmonics
and Quality of power.
[6] Jaber, Q.M. and Q.A.M. Naman, 2005, “High speed stability of induction motors at low
speeds using V/F control method. J.Eng.Sci. Assiut University, 33: 1845-1853.
[7] C.Mercer, “The analysis, simulation and control of cycloconverter drives for ship
propulsion”, Master’s Thesis Naval postgraduate school, 1996.
[8]
Y.Liu, G.Heydt, and R.Chu, “Power Quality impact of cycloconverter control strategies”,
IEEE Transactions on power delivery vol.20, no.2, April 2005, pp.1711-1718.
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